The emergence and spread of bacteria that can resist the effects of antimicrobial drugs is a major health problem. This project's long-term objective is to understand the factors that underlie antibiotic resistance in microbial populations. The investigations proposed for this project period will identify regulons whose function enables microbes to adapt phenotypically to, and circumvent the effects of, antibiotic exposure. Its goals are to discover potential targets for novel drug therapies that combat adaptive antimicrobial drug resistance and to provide an informational resource that will be broadly useful to scientists studying the adaptive resistance problem. The investigations will employ a combination of genomics and genetics approaches to achieve these goals. They will focus on adaptive antibiotic resistance in Streptomyces, a genus of morphologically complex eubacteria that produces about 60% of the world's antibiotics and is believed to be a source of multiple genes and mechanisms that lead to antimicrobial resistance in prokaryotes. There is evidence that sub-inhibitory concentrations of foreign and native antibiotics can signal the induction of normally silent genes that mediate adaptive multidrug resistance in Streptomyces. Preliminary experiments have identified several such genes by global analysis of gene expression;their evolutionary conservation suggests that orthologs of Streptomyces genes may have analogous actions in other bacterial taxons. The aims of the proposed project are to: 1) define conditions for antibiotic induction of adaptive resistance phenotypes;elucidate the spectrum of resistance phenotypes induced by structurally and mechanistically different families of antimicrobial agents;2) using methods of global analysis of gene expression and additional confirmatory procedures, elucidate gene expression perturbations occurring in bacteria exposed to antimicrobials;3) using the GABRIEL system of knowledge-based computer programs and other bioinformatics methods, identify gene expression signatures (i.e., "antibiotic stimulons") induced by antimicrobial agents;correlate signatures with the resistance phenotype and with known information about antimicrobial properties;compile a database of stimulon genes as potential targets for drugs aimed at combating adaptive resistance;identify orthologs of antibiotic stimulons in other bacterial species;4) confirm the functional role of candidate targets in antibiotic-induced resistance phenotypes;and 5) directly discover additional adaptive resistance regulators and resistance mechanisms using mutational approaches and phenotypic screening or selection. The proposed research represents a continuation and extension of experiments carried out and published during the current project period, and the experimental approaches to be used have been validated during prior work. Collectively, the proposed studies are intended to provide fundamental knowledge that is of practical use in combating adaptive antimicrobial resistance in bacteria. PUBLIC HEALTH RELEVANCE The emergence and spread of bacteria that resist the effects of anti-microbial drugs is a major health problem. This project's objective is to provide information about mechanisms that enable bacteria to adapt to antibiotic exposure and is expected to enable more effective countermeasures to be taken against microbes that persist viably during antibiotic treatment.